1. Field of the Invention
The present invention relates to an electric shaver and more particularly to an electric shaver having a plurality of cutting or shearing units.
2. Prior Art
The driving mechanism of a conventional electric shaver is shown in FIG. 7.
The shaver housing 12 is provided with an opening 12a in the head, and an outer cutter frame 30 is fastened to this opening 12a. A mounting plate 14 is installed in the shaver housing 12 apart from the outer cutter frame 30, and a single motor 16 is mounted on this mounting plate 14. The output shaft 16a of the motor 16 protrudes from the mounting plate 14, and a drive gear 18 is attached to the end of the output shaft 16a. The drive gear 18 engages with three transmission gears 20 (only one is shown) which are rotatable on the mounting plate 14 via a gear shaft. The transmission gears 20 are arranged so that they are at corners of an imaginary equilateral triangle.
Each one of the transmission gears 20 is engaged with a tubular transmission shaft 24. The tubular transmission shaft 24 has a flange 24b at the root end, and the flange 24b is set inside a guide tube 20b of the transmission gear 20. The guide tube 20b has an inwardly extending projection 20c that prevents the transmission shaft 24 from slipping out. Thus, the transmission gear 20 and the tubular transmission shaft 24 are simultaneously rotated by the motor 16. A spring 21 is installed between the tubular transmission shaft 24 and the guide tube 20b so that the tubular transmission shaft 24 is kept pushed outwardly or to the left in the drawing.
Outer cutters 36 (only one shown) are installed in the outer cutter frame 30 in an unrotatable fashion. Each outer cutter 36 has an annular shaving surface 37, and radial slits 37a are formed as hair entry openings over the entire shaving surface 37a. In addition, a groove 37b is formed in the undersurface of the shaving surface of the outer cutter 36. On the other hand, an inner cutter is attached to each one of the transmission shafts 24. The inner cutter is comprised of a central disk 39 and a plurality of arms 39a projecting from the central disk 39. Blades 40 which slide along the inner surface of the groove 37b of the outer cutter 36 are installed at the ends of the arms 39a so as to be guided by the grooves 37b of the outer cutter 36. The central disk 39 of the inner cutter is fit over the tip end of the tubular transmission shaft 24.
In the above, the outer cutter 36 and the inner cutter 38 make a shearing or cutting unit. Thus, the convention shaver described above has three shearing or cutting units.
However, the conventional electric shaver as described above has problems. The power of the single motor 16 is transmitted to three inner cutters 38 via three transmission gears 20 via a single drive gear 18. As a result, an abnormal noise is generated from the engaging portions of the gears during rotation.
More specifically, the transmission gears 20 are mounted on the gear shafts 22, and some play is inevitable. In addition, the driving force is transmitted to the respective transmission gears 20 from the single drive gear 18; as a result, the force tends to be transmitted unevenly. In other words, the driving force tends to apply onto one portion of the transmission gear 20 and not evenly to the entire circumference of the transmission gear 20. As a result, together with the play between the transmission gears 20 and the gear shafts 22, the transmission gears 20 are likely to make oscillations in the axial direction.
Such axial shifting of the transmission gears 20 is not avoidable. More specifically, the blades 40 of the inner cutters 38 are guided by the grooves 37b of the outer cutters 36, and therefore, the axes of the tubular transmission shafts 24, outer cutters 36 and inner cutters 38 can coincide by the axis shift of the tubular transmission shafts 24 in the radial direction. However, the axes of the transmission gears 20 and tubular transmission shafts 24 cannot coincide in this manner. In other words, the axes of the gear shafts 22 and the axes of the tubular transmission shafts 24, inner cutters 38 and outer cutters 36 are not able to coincide perfectly. As a result, some of the driving force is lost during transmission.
As seen from the above, the conventional shaver includes a plurality of shearing units; and therefore, when a load from shearing the hair is onto one of the shearing units, the effect of this load causes the performance of the other shearing units to drop, thus decreasing the overall performance of the shaver.
As described above, the tubular transmission shafts 24 have a structure that can absorb some axial shifting, and also the tubular transmission shafts 24 can move in the radial direction. Accordingly, the blades 40 of the inner cutter 38 are guided by the grooves 37b of the outer cutters 36, so that even if the axes of the gear shafts 22 are not perfectly aligned with the axes of the inner cutters and the outer cutters, this discrepancy can be absorbed and hairs can be sheared by the outer cutters 36 and inner cutters 38. However, if the outer cutters are dome-shaped blades or have a convex top having mesh-form hair entry holes, axial misalignment is not permissible because the dome-shaped outer cutters have curved surfaces that do not allow the inner cutters to be guided by the outer cutters.